1. Field of the Invention
The present invention relates to a server system for performing communication over a wireless network, and more particularly to a server system for performing communication over a wireless network and a communication method thereof that can reduce the number of retransmissions when a data packet is transmitted by providing a server device in which a pre-existing auto-fall back function for sequential, initial transmission rate setup is improved and the improved auto-fall back function for setting a transmission rate of the next packet is implemented on the basis of the last transmission rate of a leading packet when a data stream is sent, in wireless communication based on a transmitter-driven media access control (MAC) protocol.
2. Description of the Related Art
Conventionally, a media access control (MAC) protocol is based on one of two sub-layers classified by a multipoint connection in a local area network (LAN) requiring a line sharing/managing function. The two sub-layers include a logical link control (LLC) sub-layer and the MAC sub-layer. The MAC protocol allows a plurality of computers to share a single line. The MAC protocol widely employs an Ethernet based on Institute of Electrical and Electronics Engineers (IEEE) 802.3, a token bus based on IEEE 802.4 and a token ring based on IEEE 802.5.
The conventional MAC protocol will be described with reference to the annexed drawings. FIG. 1 is a flowchart illustrating a process for transmitting and receiving data and signals between server/client devices based on the conventional transmitter-driven MAC protocol. FIG. 2 is an explanatory view illustrating the data transmission process of a conventional server system for performing communication over the wireless network. An operating method of the conventional server system and the drawbacks thereof will be described with reference to FIGS. 1 and 2.
FIG. 1 shows flow of signals transmitted and received between the server/client devices. The server device to send data, that is, a transmitting stage (Tx), transmits a request-to-send (RTS) signal to a corresponding client device to receive data, that is, a receiving stage (Rx) (at the step of transmitting the RTS signal).
The client device receives the RTS signal from the server device. Subsequently, the client device transmits, to the server device, a clear-to-send (CTS) signal indicating that data can be sent, in response to the RTS signal (at the step of responding to the RTS signal).
After the RTS and CTS signals are exchanged, the server device sends data to the client device over a set communication channel (at the step of sending the data). The client device receiving the data sends a positive acknowledgement (ACK) signal to the server device when the data has been completely received (at the step of transmitting the ACK signal).
FIG. 2 is an explanatory view illustrating a process for sending a data packet from the server device during data communication between the server and client devices. First, the server device transmits a first request-to-send (RTS) signal RTS1 to a corresponding client device to receive data. The client device receives the first RTS signal RTS1 and then transmits a first clear-to-send (CTS) signal CTS1 to the server device.
After the RTS and CTS signals are exchanged, the server device initiates a data transmission operation and sends a data packet #0_6. Here, “0” denotes a packet number and “6” denotes the number of retransmissions. The data packet #0_6 indicates that the server device has sent a packet having the packet number “0” to the client device six times after the first packet transmission.
When the client device transmits a negative acknowledgement (NAK) signal NAK1 in spite of 6 retransmissions, the server device transmits a second RTS signal RTS2 for 7th retransmission. Upon receiving a second CTS signal CTS2, the server device sends a data packet #0_7.
When the client device has completely received the data packet #0_7 normally, it transmits a positive acknowledgement (ACK) signal ACK2. The server device transmits a third RTS signal RTS3 to send the data packet #1_0. The client device transmits a third CTS signal CTS3 in response to the third RTS signal RTS3.
In a data transmission operation of the conventional server system, the server device implements an auto-fall back function while sequentially scanning transmission rates of 11 Mbps, 5.5 Mbps, 2 Mbps and 1 Mbps according to a distance between the server device and the client device. A transmission rate based on the conventional auto-fall back function will be described with reference to FIG. 2.
As the distance between the client device and the server device is long, the data packet #0_6 is sent over a communication channel based on a transmission rate of 1 Mbps as shown in FIG. 2. Moreover, when the data packet #0_6 has not been received, a data packet #0_7 is sent at the transmission rate of 1 Mbps.
When the client device has received the data packet #0_7, the server device sends a new data packet #1_0. In spite of a substantial data transmission rate of 1 Mbps, data begins to be sent at a transmission rate of 11 Mbps according to the conventional auto-fall back function.
Because a network environment at the time of transmitting a previous data packet is not considered in the conventional auto-fall back, a transmission rate of 11 Mbps is fixedly set whenever an operation for sending a new data packet is initiated. For this reason, a wireless network environment cannot be effectively employed, and the number of unnecessary retransmissions is increased. Moreover, data transmission is delayed or a data error is incurred, and the wireless network environment appropriate for multimedia streaming cannot be implemented.